MSefi.com read only forum (Jan.15,2018)

The returnless 58 PSI fuel system used on '99-'03 Corvettes is very popular with hot roddres and good to about 600 HP. It is very stable, just not manifold-referenced. Since we have a VE table based on MAP anyway, why can't we fudge the low pressure values down slighlty to fully compensate for the fuel pressure differential across the injectors.

I have such a setup and I was thinking I'd have to swap it out for a conventional return system to use MS.

Quick back of the envelope calculations would indicate that for 58 psi, you'd have to lean out your VE by 9% at 25 kPa. There is no danger of a lean detonation while tuning, because if undercompensated, you'd only get richer with load.

Mike

Many MSers have used non-referenced regulators with fixed rail pressures. While MS 'expects' there to be a fixed differential between the MAP and rail, you can generally tune around it with full control. Go for it.

David

if gm can do it you can too just do like you were saying and if you don't take enough it will be rich and you can take out a little more at a time till you get it right a good wide band would make it easy but you could probably get it to drive ok by ear Zane

The only issue with using a returnless configuration is related to the injector pulse resolution. For a naturally aspirated engine with a manifold pressure range of say 0.2-1 atmosphere, there shouldn't be too much trouble so long as the injectors are not overrated for the engine (otherwise it may be hard to get a stable idle mixture). For a pressure fed engine there may be issues.

With manifold reference the amount of fuel injected per cycle (turndown ratio) varies over about a 5:1 - 6:1 ratio (more for a blown engine). With a fixed fuel pressure (relative to atmospheric) the turndown ratio may be more like 15:1 - 25:1 for an NA engine. I would suggest that you'll need MS1/Extra or MS2, the original MS1 might not have enough injector resolution (I think it's 0.1ms or something, probably too big a step).

Cheers

yeah this is true or aeromotive and some other companies make a voltage controller for the pump similar to what oem uses but i'm guessing that would do away the cheap cause i already got it to use method of the setup. Zane